Method of molding prestressed concrete structures



y 20, 1952 J. HUDDLESTON 2,597,084

METHOD OF MOLDING PRESTRESSED CONCRETE STRUCTURES.

Filed Jan. 13, 1948 2 SHEETS-SHEET 1 INVENTOR. JUL M/v 144mm 5 701v BY -"m y 1952 J. HUDDLESTON 2,597,034

METHOD OF MOLDING PRESTRESSED CONCRETE STRUCTURES Filed Jan. 15, 1948 2 SHEETS-SHEET 2 INVENTOR. JUL/AN M10045 ra/v BY I I Patented May 20, 1952 METHOD OF MOLDING PRESTRESSED CONCRETE STRUCTURES Julian Huddleston, Los Angeles, Calif. Application January 13, 1948, Serial No. 2,017

Claims. 1

My invention relates to the production of structures from cementitious material reinforced where necessary by high tensile strength members such as iron or steel hoops or bands.

While cementitious materials have satisfactory strength in compression for structural uses, they have little strength in tension, but by the use of steel reinforcing rods to take the tension stresses, a wide variety of structures may be advantageously erected using cementitious materials.

It is a particular object of my invention to provide a method of producing circular tanks of cementitious material having a prestressed wall construction so constructed that the wall will not be under tension at any time.

In present methods of building prestressed tanks of cementitious material, it has not been found possible to evenly distribute the stresses of the steel reinforcing hoops, whereas by my method of construction, the reinforcing hoops are brought individually to a predetermined value of tension which is utilized to set up an evenly distributed inward acting stress in the wall which is permanently retained.

Great numbers of circular metal tanks of large size are used but are expensive to maintain since the metal must be protected against corrosion both by the contained fluid and by the atmosphere. terial construction, on the other hand, require practically no maintenance, but have not hitherto come into wide use since a suitable method of construction to produce tanks competitive in final cost'with metal tanks has not previously been provided.

It is, accordingly, a particular object of my invention to provide a circular tank construction utilizing cementitious material which may be rapidly and inexpensively erected and will be as satisfactory in service as a metal tank while costing much less to maintain.

Still further objects and features of my invention will hereinafter appear from the following description taken in conjunction with the accompanying drawings.

In the drawings;

Fig. 1 is a perspective view of a circular liquid containing tank of cementitious material having a suspended roof of similar material, a portion of the wall being broken away to show the arrangement of reinforcing members;

Fig. 2 is a fragmentary section on the line 22 of Fig. 1 to an enlarged scale;

Fig. 3 is a fragmentary section on the line 3-3 of Fig 2; 1 U

Tanks of reinforced cementitious ma- Fig. 4 is a perspective view showing the use of a tool of my invention utilized in the method'of my invention; I

Fig. 5 is a fragmentary view in side elevation and to a larger scale showing the tool in initial applied position;

Fig. 6 is a view similar to Fig. 5 showing the tool in operative position;

Fig. '7 is a view taken on the line 1-1 of Fig. 5.

In the drawings, the numeral 2 indicates a tank of reinforced cementitious material standing upon a cement floor and wall footing 22 and having a suspended top 24. The construction of the watertight joint of the walls with the floor may be of any satisfactory type such as are known in the art of building cement structures and is, therefore, not thought to require particular description or illustration.

The tank top 24 is provided with the usual inspection manhole with cover 26 and bottom outlet port 28 closed by a bolted down plate.

In order to prevent rain from accumulating in the inwardly and downwardly curved suspended roof, I provide a drain pipe 30 connected to an outlet at the bottom of the roof or top, the outlet being covered by a wire mesh strainer 32.

My improved tank construction involves the following steps after the cement floor and footing has been provided.

First, a circular single wall form of the proper diameter and height is set up on the floor with vertical reinforcing mesh 34 spaced radially inward from the form wall. The mesh may be supported from the form by soft iron wires looped around the wire mesh and extended through the form and the outer ends may be twisted around vertically arranged rods 36 or light metal strips which are left to be later covered by a second'or outer layer of cement. The rods may serve during the erection of the inner layer 38 of the wall as supports for the forms.

Upwardly and outwardly extending pins 40 are secured to the rods or strips 36 by being welded thereto at intervals in their height for a purpose to be later explained.

The inner surface of wall 38 is then built up, as for instance, by spraying an atomized fine mixture of cementitious material onto the inner face of the form until a predetermined thickness has been built up whereupon the inner portion of the wall is allowed to set sufficiently to permit the next step of the method to be put into operation.

It is to be understood that I do not limit myself to a process of spraying a cementitious'mixture onaform to build up the inner portion .0!

the wall since I may prefer to form the inner portion of the wall by positioning inner and outer forms and pour cement or concrete material between the forms, with or without the use of vertical steel reinforcing rods. If reinforcing rods are not used, pins 40 are driven directly into the inner portion of the wall after removal of the forms.

The secondstep in my novel method of construction involves placing the inner portion of the wal1 under a predetermined degree of compression, this object being in part achieved preferably, although not necessarily, bythe use of a tensioning tool of my invention.

A series of steel hoops 42 are bent around the exterior surface of the wall, each hoop being located at a predetermined height by the appro priate peripheral series of projecting pins 40. The meeting ends of the hoops are joined together permanently, as for instance, by Welding,

' The hoops are, then caused to exert a predetermined pressure on the wall by tensioning the hoops at a plurality of points by the use of a tool generally indicated at 42, and then inserting a series of steel wedges 44 While the hoops are under stress, between the hoops 41 and the wall at appropriate distances from each other, with the wedges in each series preferably staggered with respect to the wedges in the series above and below. The inner portion of the wall is thus brough n o a 1 11 1 561 on ion.-

The third step of my method of constructing tanks of cementitious material is to build up the outer portion of the wall to completely embed the compression applying members and thus avoid the necessity for otherwise protecting the metal members of the construction. I prefer to build up this wall by the process of spraying atomized fine concrete or cement until the requisite thickness. has been obtained because of the greater speed and cheapness of this method.

The forms utilized may be of any suitable construction but that preferredby me comprises sheets of corrugated metal such as galvanized iron used with the corrugations running vertie cally. This material is flexible so that it may be shaped readily to set up formsfor the construction of tanks of various diameters and is largely selfsupporting, thus reducing" the work necessaryand aniount of material required to b ild rigid forms. Further, the corrugated sheets can bereadily treated to prevent the adherence f concr t or cem n h reto a dj il in definitely in service.

The. steps so far described complete theiormationn a nk; wi a res W d i same casesinay provide the oompletetanls if no cover when s re re Fi s 4 through 7 illustrate a suitabletoollfioi my invention by the use of which the hoops 42, which are each complete rings, may be readily brou ht, to a re et rm n d e It wi l evident that the inward stress exerted on the tank wall may be controlled as desired. Since the outward thrust exerted by the liquid on the wall will be inproportion to-its head, the thrust will be more tow rd. t bo t m of he ta k ha toward the top- This iat n n s r s d s b t o m y be provided for by varying the spacing of the hoops which is the-simplest method, or by mparting a progressively greater tension to the hoops toward the bottom of the tank.

The-tool 46 is formed as a two part lever, the outer length Miaof the lever beingyieldably connetted to the innerlength 46b of, the. lever. The.

yieldable connection of the inner and outer arms of the lever may be formed by plates 48 and 49 hinged together at one end by a pin 50 and held together by a spring 5| mounted on a pin 52 secured in one plate 49, the spring being placed under compression between a nut 53 threaded on pin 52 and the other plate 48. The tension of the spring 5| may be adjusted b nut 53, the usual c ut, o ho b in rovid d. tgprevent slacking back of nut 5!. The inner end of arm 46b is provided with a hoop engaging jaw 54 and is pivoted to a fulcrum piece 56 by pin 58. The fulcrum piece isformed as a foot having spaced supporting flanges 60,61. The lever is pivoted toward one side of the foot, the adjacent flange 60 of the fulcrum piece being jaw shaped to oooperate with jaw- 54 in grippin the hoop 42. Flange 6 I carries the thrust of the lever when the tool is in operation.

he. tool. 46 used. by e ing Jews .4 andi with a ow and then a n dawn on th lever nti lat s i s b sin' separatea th edge opposite to the hinge. The position of the hoop engaging parts. while tensioning a hoopis shown in Fig. 6. It will be noted that the lever forms a lever of the. third order and is arranged to provide a very large transmission of force to the hoop for a moderate pressure on. the handle.

It, is, of course, possible toattain thepredeters mined tension in the hoops by the use of the wedges alone and the use of any convenient tension determining instrument to indicate when the predetermined value of the tension has been reached.

Most tanks are required to becovemd by and my invention contemplates a suitable cover or root of cementitious material arranged so that thestresses imposed on the walls are eompressive, thus. utilizing the. inherent strength of the na-f terial, and also eliminatingthe cost, of the usual method of constructing the forms.

1 claim:

1. A method of forming structures with walls of cementitious material comprisingi erecting. a form for a wall; erecting said wall} applying a eries l s m al an a ued h 'n'e i r-y i the l p es ressins e h an a: a 1 a itv sp ce m nis b a lyin a re e ermia iierse to th bend. i a ire ti n n ma is the wa ap l ing bi e be een he b a s as Wend @911 re tressed seame 9,? 21 .2%1115 i9 h rees bii heq ress 9 S id beads. a d st el d sirihuta a d stress. ascend hawed, and emb ddin the h esire sd e as and said blocks in a layer of protective ljIiQtQl-lgl.

a mine at iqrmin irgqi ies w iwa 9 cementi iqus ma ri l q gi s n a e set ste fo a Wa static a e e itiii a e 3 wai arran in a plur t 9i Wa dlmrmmiins p ns in ced p a el as a the 9s: riphery f said well; a plyin eadl ssigeial and on ach peri hera se ies. 1- tei me prest e s ns each. hand a spac d .91. ns: a p dete m ned force to. instead dimtion normal to the wall; inserting wedges between the bands and said wall at each prestressedpeint t a n a n t r d t minedstresse n v i tributed a ound sai Wel nd-embeddin the p es e s ci bands. and w es. na a er- 0.113. 7 teotive m te a ormin an ou er wa 3. A method of formingprestressed cemgntig tious structures consistinggof-z erection of" an internal form of a shape corresponding toithat of, the desired structure, applicationof plastic ma- :5 terial to the exterior of said form to forman inner wall of desired thickness, application of metallic reinforcing and tensioning rods circumferentially to the exterior of said inner wall after the material has set, permanently joining the ends of said rods to form vertically spaced endless bands, prestressing each band at a plurality of circumferentially spaced points by applying a predetermined force to the band in a direction normal to the wall, inserting elements between said endless bands and said inner wall at certain of said prestressed points to hold the bands in prestressed condition, and spraying a plastic material on to and for embedding said prestressed bands and said holding elements, so as to maintain said structure compressed against possibility of fracture and collapse occasioned by undue stress from the interior of the structure.

4. A method of forming prestressed cementitious structures consisting of erection of an internal form of a shape corresponding to that of the desired structure, application of plastic material to the exterior of said form to form an inner wall of desired thickness, application of metallic reinforcing and tensioning rods circumierentially to the exterior of said inner wall after the material has set, permanently joining the ends of said rods to form vertically spaced endless bands, prestressing each band at a plurality of circumferentially spaced points by applying a predetermined force to the band in a direction normal to the wall, inserting elements between said rods and said inner wall at certain of said prestressed points to hold the bands in prestressed condition, and spraying a plastic material on to and for embedding said prestressed bands and the interior of the structure, said holding elements being staggered in position to adjacent band positions.

5. A method of forming a tank structure having a substantially cylindrical cementitious wall comprising: erecting a form for the wall; erecting said wall; applying a series of endless metal hoops around the outer periphery of said wall, prestressing each hoop at a plurality of circumferentially spaced points by applying a predetermined force to the hoop in a direction normal to the wall; applying blocks between the hoops and the wall at each prestressed section of the hoop to maintain the preestablished stress of said hoops and evenly distribute said stress around the wall; and embedding the prestressed hoops and said blocks in a layer of protective material.

JULIAN HUDDLESTON.

REFERENCES QITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 772,117 W'inslovr Oct. 11, 1994 1,062,736 Rechniewski May 27, 1913 1,367,289 \Valler Feb. 1, 1921 1,584,658 Rutten May 11, 1926 1,910,642 Sherrard May 23, 1933 1,992,511 Smith Feb, 26, 1935 2,185,749 Kennedy Jan. 2, 1940 2,315,894 Crom Apr. 6, 1943 2,326,010 Crom Aug. 3, 1943 2,329,719 Hewett Sept. 21, 1943 2,355,947 Bondy Aug. 15, 1944 2,418,580 Crom Apr. 8, 1947 2,470,009 Wilhelm May 10, 1949 

